Interconnect structure with barrier layer

ABSTRACT

Low capacitance and high reliability interconnect structures and methods of manufacture are disclosed. The method includes forming a copper based interconnect structure in an opening of a dielectric material. The method further includes forming a capping layer on the copper based interconnect structure. The method further includes oxidizing the capping layer and any residual material formed on a surface of the dielectric material. The method further includes forming a barrier layer on the capping layer by outdiffusing a material from the copper based interconnect structure to a surface of the capping layer. The method further includes removing the residual material, while the barrier layer on the surface of the capping layer protects the capping layer.

FIELD OF THE INVENTION

The invention relates to semiconductor structures and, moreparticularly, to low capacitance and high reliability interconnectstructures and methods of manufacture.

BACKGROUND

Microelectronic devices are made of transistors and the interconnectionsystem connecting them to make a circuit. An interconnection system maycomprise lines at multiple levels connected by vias. As devicedimensions shrink at both the transistor and interconnection systemlevels, many technical challenges arise. For example, two technicalchallenges of the interconnection system level include the reduction ofinterconnect resistive-capacitive (RC) delay and the increase inreliability (electromigration (EM) and time-dependent dielectricbreakdown (TDDB)). By way of example, a circuit signal delay may bedominated by the RC delay in the interconnect system, when there aresmaller distance between the lines of the interconnect system.

In order to reduce the capacitance, low dielectric (low-k) materials canbe used, in addition to minimizing the dielectric constant of the capdielectric material which has a diffusion barrier function to Cu and Odiffusion, such as SiCN, SiN and SiC. However, the implementation oflow-k dielectrics is limited because of the difficulty in itsintegration in fine dimensions. Also, the minimization of the dielectriccap material is limited because the material functions as an etchingstop layer for via etching for interconnects in the upper level.

SUMMARY

In an aspect of the invention, a method comprises forming a copper basedinterconnect structure in an opening of a dielectric material. Themethod further comprises forming a capping layer on the copper basedinterconnect structure. The method further comprises oxidizing thecapping layer and any residual material formed on a surface of thedielectric material. The method further comprises forming a barrierlayer on the capping layer by outdiffusing a material from the copperbased interconnect structure to a surface of the capping layer. Themethod further comprises removing the residual material while thebarrier layer on the surface of the capping layer protects the cappinglayer.

In an aspect of the invention, a method comprises: forming anelectroplated copper interconnect structure in an opening of adielectric material; selectively forming a capping layer on the copperbased interconnect structure which results in residual material formingon a surface of the dielectric material; oxidizing the capping layer andthe residual material by exposing the capping layer and residualmaterial to air; forming a barrier layer on the capping layer byoutdiffusing Mn to a surface of the capping layer; and removing theoxidized residual material with a selective etching process.

In an aspect of the invention, an interconnect structure comprises: acopper interconnect structure formed in a dielectric material; a cappinglayer in contact with a top surface of the copper interconnectstructure; and a barrier layer outdiffused on a surface of the cappinglayer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1-5 show fabrication processes and respective structures inaccordance with aspects of the present invention;

FIGS. 6-9 show fabrication processes and respective structures inaccordance with additional aspects of the present invention; and

FIG. 10 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

The invention relates to semiconductor structures and, moreparticularly, to low capacitance and high reliability copper (Cu)interconnect structures and methods of manufacture. More specifically,the present invention provides a barrier layer, e.g., MnO or MnSiO, onthe interconnect structure (e.g., capping layer) to protect theinterconnect structure during removal of any residual material ondielectric material that would otherwise cause electron flow paths orline to line leakage. Advantageously, the present invention will thusreduce RC and improve reliability (e.g., electromigration (EM) andtime-dependent dielectric breakdown (TDDB)) in copper nano-interconnectdevice structures.

Electromigration (EM) is dominated by the interface diffusion at the capdielectric/copper interface. One of the approaches to improve the EM isto cap the top surface of the copper interconnect with metal such as Coand CoWP. However, these metal caps need to be formed selectively on topof Cu without any deposition of or contamination with the metal atoms onthe dielectric surface between Cu lines. Any break in selectivitycreates the TDDB problem between neighboring Cu lines such as theformation of surface defects that cause imperfect metal cap depositionselectivity. The present invention solves this problem by providingstructures and respective fabrication processes to remove any residualmaterials formed from the deposition of metal on the dielectricmaterial, resulting from the selective deposition process on theinterconnect structure.

The copper interconnect structures of the present invention can bemanufactured in a number of ways using a number of different tools. Ingeneral, though, the methodologies and tools are used to form structureswith dimensions in the micrometer and nanometer scale. Themethodologies, i.e., technologies, employed to manufacture the copperinterconnect structures of the present invention have been adopted fromintegrated circuit (IC) technology. For example, the structures of thepresent invention are built on wafers and are realized in films ofmaterial patterned by photolithographic processes on the top of a wafer.In particular, the fabrication processes of copper interconnectstructures uses three basic building blocks: (i) deposition of thinfilms of material on a substrate, (ii) applying a patterned mask on topof the films by photolithographic imaging, and (iii) etching the filmsselectively to the mask.

FIG. 1 shows a structure and respective processing steps in accordancewith aspects of the present invention. More specifically, the structure5 of FIG. 1 includes an interconnect structure comprising multiplelayers of material as shown by reference numeral 10. By way of exemplaryformation processes, an opening is formed in a dielectric layer 12 usingconventional lithography and etching processes. For example, a resist isformed over the dielectric layer 12, which is then exposed to energy(light) to form a pattern. The via is then formed in the dielectriclayer 12 through the opening, using conventional reactive ion etching(RIE) processes.

After formation of the opening, an underlying barrier layer 14, forexample, Tantalum Nitride (TaN) may be deposited in the via using, forexample, a plasma vapor deposition (PVD) process or chemical vapordeposition (CVD) process. In embodiments, the underlying barrier layer14 coats the sidewalls and bottom of the opening. Thereafter, a coppermanganese (CuMn) layer 16 is deposited on the underlying barrier layer14. In embodiments, the CuMn layer 16 is deposited to a thickness ofabout 50 Å to 500 Å using PVD processes; although other dimensions arealso contemplated by the present invention. The percent Mn of the CuMnlayer is less than 20 atomic percent and preferably in the range ofabout 0.5% to about 20% atomic percent, depending on device application.

In embodiments and according to experimental results, below 0.5% atomicpercent, e.g., 0.35% atomic percent, the Mn percentage is not enough forMn segregation to take place. On the other hand, one upper limit can beabout 10% atomic percent. This is because Mn atoms which reside in Cueven after parts of Mn atoms are consumed for the formation of Mnsegregated layer will increase the Cu interconnect resistance due to theimpurity scattering effect. It should be understood, though that smallerthe increase of the line resistance will result with a smaller linewidth. Accordingly, when the line width is 7 nm, the resistance increasedue to the residual Mn atoms is calculated as 10% when the Mn % is 10%atomic percent. In this way, the 10% atomic percent is set as the upperlimit in practical cases; however, it is up to device application howmuch increase in line resistance is acceptable. From this standpoint,the range can be set at less than 20% atomic percent. In view of theabove, it should be understood that the range of Mn percentage iscritical, as there must be enough Mn to form the later described layers,but not too much in order to maintain a low resistance of the copperinterconnect.

Still referring to FIG. 1, a copper interconnect 18 is then formedwithin the remaining open space of the opening. In embodiments, thecopper interconnect 18 is formed by an electroplating process. In someelectroplating embodiments, the CuMn layer may be used as a seed layerfor the electroplating process. The entire structure 10 undergoes a lowtemperature annealing process to grow copper grains. In embodiments, thelow temperature anneal process is at about 100° C. for about 1 hour. Anyexcess material on a top surface of the dielectric layer 12 is removedusing, for example, a chemical mechanical process (CMP).

In FIG. 2, a capping layer 20 is formed on the interconnect structure10. In embodiments, the capping layer 20 can be cobalt or CoWP depositedby a selective deposition process to the copper layer 18. Inembodiments, the selective deposition process may result in residualcobalt (or CoWP) 22 being deposited on the dielectric layer 12. Inalternate embodiments, the capping layer 20 can be, for example, Ru, Ag,Zn, Sn or Ni, resulting in residual material of Ru, Ag, Zn, Sn or Ni. Inthis alternative embodiment, the underlying barrier layer 14 may be alayer of cobalt. In any of these cases, the residual material 22 willneed to be removed (as is discussed later), without removal of thecapping layer 20.

In FIG. 3, the structure of FIG. 2 and more specifically the cappinglayer 20 and residual material 22 undergo an oxidation process. Inembodiments, the oxidation process can be performed by exposing thecapping layer 20 and residual material 22 to air for about 2 hours ormore. In embodiments, the oxidation process can be accelerated by anannealing process. In the case of the selective deposition of cobalt forthe capping layer 20, the oxidation process will result in a CoO (cobaltoxide) passivation layer 24, coating the capping layer 20 and residualmaterial 22. In the case of Ru, Ag, Zn, Sn or Ni as being used as thecapping layer 20, the oxidation process will result in an oxidizedpassivation layer 24, e.g., RuO, AgO, SnO, NiO, or ZnO, coating thecapping layer 20 and the residual material 22.

As shown in FIG. 4, the structure undergoes an annealing process to forma self aligned barrier layer 26 on top of the capping layer 20. Inembodiments, the annealing process is performed at about 300° C. toabout 400° C. The annealing process will result in a MnO barrier layer26 due to outdiffusing of the Mn through the copper layer 18 and capping(Co, or CoWP or Ru, Ag, Zn, Sn or Ni) layer 20. In further embodiments,in the case in which the deposition of the dielectric material 12 isperformed in an ambient containing SiH₄ or Si₂H₆ or molecules whichsupply Si, the barrier layer 26 can be MnSiOx; instead of a MnO. Itshould be understood by those of skill in the art that the annealingwill not affect the oxidized passivation layer 24 on the residualmaterial 22 regardless of the materials used for the capping layer 20.This is due to the fact that Mn will not outdiffuse through thedielectric layer 12.

In FIG. 5, the residual material 22 and accompanying passivation layer(oxidized layer) 24 can be removed by a dry or wet etching process. Inembodiments, the removal may be selective to the dielectric material 12.For example, in embodiments, dilute solution of HF can be used in theetching process to remove the residual material 22 and accompanyingpassivation layer 24, without removing of the dielectric layer 12 or thecapping layer 20. In this way, by removing only the residual material22, leakage issues, electron flow paths as well as TDDB issues can beeliminated.

It should be understood that the MnO (or MnSiOx) barrier layer 26 willprotect the capping layer 20 during the etching process such that onlythe residual material 22 (between Cu lines) is removed. Also, the MnO orMnSiOx barrier layer 26 blocks the oxidation of capping layer 20 uponvacuum break, which prevents wet attack of the capping layer 20 insubsequent level post RIE via cleaning steps (which could otherwiseundercut the structure by etching the capping layer 20).

FIGS. 6-9 show fabrication processes and respective structures inaccordance with additional aspects of the present invention. In thisembodiment, the structure 5 includes an interconnect structure 10′comprising a first layer 14′ of cobalt, followed by a layer of CuMn 16and a copper layer 18. The layers 14′, 16 and 18 can be formed in thesimilar processes as already described herein, e.g., PVD, CVD andelectroplating. A capping layer 20 is formed on the interconnectstructure 10′. In embodiments, the capping layer 20 can be cobalt orCoWP, deposited by a selective deposition process as already describedherein. Alternatively, the capping layer 20 can be, for example, Ru, Ag,Zn, Sn or Ni. In this alternative embodiment, the cobalt layer 14′ canbe replaced with a layer of Ru, Ag, Zn, Sn or Ni, respectively. In anyof these embodiments, residual material 22 is formed on the dielectricmaterial 12, as described with reference to FIG. 2.

In FIG. 7, the structure of FIG. 6 and more specifically the cappinglayer 20 and residual material 22 undergo an oxidation process. Inembodiments, the oxidation process can be performed by exposing thecapping layer 20 and residual material 22 to air for about 2 hours ormore. In embodiments, the oxidation process can be accelerated by anannealing process. In the case of the selective deposition of cobalt forthe capping layer 20, the oxidation process will result in a CoO (cobaltoxide) passivation layer 24′, coating the capping layer 20 and residualmaterial 22. In the case of Ru, Ag, Zn, Sn or Ni as being used as thecapping layer 20, the oxidation process will result in an oxidizedpassivation layer 24, e.g., RuO, AgO, SnO, NiO, or ZnO, coating thecapping layer 20 and the residual material 22.

As shown in FIG. 8, the structure undergoes an annealing process to forma self-aligned barrier layer 26′ on the capping layer 20 and thesidewalls of the interconnect structure 10 (e.g., lining of the via). Inembodiments, the annealing process is performed at about 300° C. toabout 400° C. The annealing process will result in a MnO barrier layer26′ due to outdiffusing of the Mn through the copper layer 18 and cobalt(or CoWP) layers 14′ and 20. In further embodiments, in the case inwhich the deposition of the dielectric material 12 is performed in anambient containing SiH₄ or Si₂H₆ or molecules which supply Si, thebarrier layer 26′ can then be MnSiOx; instead of a MnO. It should beunderstood by those of skill in the art that the annealing will notaffect the oxidized passivation layer 24′ on the residual material 22regardless of the materials used for the capping layer 20. This is dueto the fact that Mn will not outdiffuse through the dielectric layer 12.

In FIG. 9, the residual material 22 and accompanying passivation layer(oxidized layer) 24 can be removed by a dry or wet etching process. Forexample, a dilute solution of HF can be used in the etching process toremove the residual material 22 and accompanying passivation layer 24.It should be understood that the MnO (or MnSiOx) barrier layer 26 willprotect the capping layer 20 during the etching process. In this way,any leakage issues or electron flow paths can be eliminated.

By implementing the processes of the present invention, a double layeredstructure of MnO(Si)/Co(WP) on top of Cu lines, i.e., MnO(Si)/Co(WP)/Cuprovides the Cu interconnect system with high EM reliability (Note,here, the parenthesis indicate the elements are optional). This is dueto the top surface of the Cu interconnect having an interface with themetal cap of Co or CoWP. And, as should be understood, without thecapping layer 20, MnO or MnSiO would be formed directly on top of coppersurface which would allow void nucleation and its diffusion duringcurrent stressing more than the metal/metal interface.

FIG. 10 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test. FIG. 10 shows a block diagram of anexemplary design flow 900 used for example, in semiconductor IC logicdesign, simulation, test, layout, and manufacture. Design flow 900includes processes, machines and/or mechanisms for processing designstructures or devices to generate logically or otherwise functionallyequivalent representations of the design structures and/or devicesdescribed above and shown in FIGS. 1-9. The design structures processedand/or generated by design flow 900 may be encoded on machine-readabletransmission or storage media to include data and/or instructions thatwhen executed or otherwise processed on a data processing systemgenerate a logically, structurally, mechanically, or otherwisefunctionally equivalent representation of hardware components, circuits,devices, or systems. Machines include, but are not limited to, anymachine used in an IC design process, such as designing, manufacturing,or simulating a circuit, component, device, or system. For example,machines may include: lithography machines, machines and/or equipmentfor generating masks (e.g. e-beam writers), computers or equipment forsimulating design structures, any apparatus used in the manufacturing ortest process, or any machines for programming functionally equivalentrepresentations of the design structures into any medium (e.g. a machinefor programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 10 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 1-9. As such,design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-9 to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information.

Design process 910 may further include, for example, standard mechanicaldesign processes such as stress analysis, thermal analysis, mechanicalevent simulation, process simulation for operations such as casting,molding, and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.

Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-9. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-9.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.,information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-9. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. An interconnect structure comprising: a copperinterconnect structure formed in a dielectric material, the copperinterconnect structure on and contacting a CuMn layer; a capping layerin contact with a top surface of the copper interconnect structure,wherein an interface of a bottom surface of the capping layer and thetop surface of the copper interconnect structure is co-planar with a topsurface of the dielectric material; and a barrier layer outdiffused onan upper surface of the capping layer, the barrier layer comprising Mnoutdiffused from the CuMn layer.
 2. The interconnect structure of claim1, wherein the capping layer is Ru, Ag, Zn, Sn or Ni and the barrierlayer is MnO.
 3. The interconnect structure of claim 2, furthercomprising a barrier layer at an interface of the copper interconnectstructure and the dielectric material.
 4. The interconnect structure ofclaim 1, wherein the capping layer is cobalt and the barrier layer isMnO.
 5. The interconnect structure of claim 4, further comprising abarrier layer at an interface of the copper interconnect structure andthe dielectric material.
 6. The interconnect structure of claim 5,wherein the capping layer is oxidized.
 7. The interconnect structure ofclaim 6, wherein the copper interconnect structure comprises: a layer ofTantalum Nitride (TaN); a layer of CuMn on the TaN layer; and anelectroplated copper layer on the CuMn layer; and the barrier layercomprises outdiffusing Mn to a surface of the capping layer during ananneal process.
 8. The interconnect structure of claim 6, wherein thecopper interconnect structure comprises: a layer of Ru, Ag, Zn, Sn orNi; a layer of CuMn on the Ru, Ag, Zn, Sn or Ni layer; and anelectroplated copper layer on the CuMn layer; and the barrier layercomprises Mn outdiffused from the CuMn layer to the surface of thecapping layer during an anneal process.
 9. The interconnect structure ofclaim 6, wherein the copper interconnect structure comprises: a layer ofcobalt; a layer of CuMn on the cobalt layer; an electroplated a copperlayer on the CuMn layer; and the barrier layer comprises Mn outdiffusedfrom the CuMn layer to the surface of the capping layer during an annealprocess.
 10. The interconnect structure of claim 9, wherein the barrierlayer is formed at an interface of dielectric material and the cobalt.11. The interconnect structure of claim 1, wherein the capping layerextends entirely across a topmost surface of the copper interconnectstructure.
 12. An interconnect structure comprising: a dielectricmaterial; an underlying barrier layer on and contacting the dielectricmaterial; a CuMn layer on and contacting the underlying barrier layer; acopper layer on and contacting the CuMn layer; a capping layer on andcontacting the electroplated copper layer, the capping layer comprisingCo; and a barrier layer on and contacting an upper surface of thecapping layer, the barrier layer comprising Mn outdiffused from the CuMnlayer, wherein the capping layer extends entirely across a topmostsurface of the copper layer; and an interface of a bottom surface of thecapping layer and the top surface of the copper interconnect structureis co-planar with a top surface of the dielectric material.
 13. Theinterconnect structure of claim 12, wherein a percent Mn of the CuMnlayer is in a range of between 0.5 and 20 atomic percent.
 14. Theinterconnect structure of claim 12, wherein a topmost surface of thecapping layer is higher than a top surface of the dielectric material.15. The interconnect structure of claim 12, wherein: the underlyingbarrier layer, the CuMn layer, and the copper layer are in an opening ofthe dielectric material; and the capping layer and the barrier layer areoutside the opening of the dielectric material.